design space pruning heuristics and global optimization method for ...

provide clues to the nature of the early solar system processes and conditions, as these are
often preserved on small bodies such as asteroids, comets, or meteorites. The near-Earth
asteroids are of particular interest because they are believed to contain clues to the nature
of the building blocks from which the inner planets were formed. Finally, the NEAR
mission was interested in measuring the properties of 433 Eros, in order to establish a
connection between meteorites and the history of asteroids, to better quantify the nature
of their impact hazard to Earth. NEAR was able to achieve these science goals with the
use of a high-thrust propulsion system. The goal of the Dawn mission, which intends to
orbit the asteroids Vesta and Ceres, is to better understand the conditions and processes
present in the early solar system4. Dawn uses low-thrust propulsion, in the form of an ion
propulsion system adapted from the Deep Space 1 mission. The propulsion system uses
Xenon propellant, and can achieve a maximum thrust level of 92 mN and a maximum
specific impulse (I sp ) of 3200 s. Dawn launched in September of 2007 and conducted a
Mars gravity assist in February of 2009. The spacecraft will arrive at the first asteroid,
Vesta, in August, 2011. After a nine month stay at Vesta, the spacecraft will depart for
Ceres, and arrive in February, 2015.
The Global Trajectory Optimization Competition (GTOC) was created in 2005 as
an example of the types of challenges mission designers face when designing low-thrust
trajectories to multiple bodies in the solar system. Since its inception, there have been
four editions of competition, all dealing with designing low-thrust trajectories to
asteroids. In each competition, entrants were given four weeks to solve the problem.
GTOC1 required participants to maximize the change in semi-major axis of the asteroid
2001 TW229 by impacting it with an electric-propelled spacecraft. 7 The spacecraft could
employ both thrusting and planetary gravity assists en route to the asteroid, while trying
v v
to maximize the following quantity: J = m U ⋅
. In the objective function
equation, m f is the final mass of the spacecraft, U v
f
rel
rel
ast
is the velocity of the spacecraft
2